1. Complex of antibodies with Hen Eggwhite Lysozyme. The complex of the recombinant form of the Fab of the HyHEL-5 antibody with lysozyme has been crystallized. These crystals diffract to a resolution of 1.7A, vs 2.6A for the previous, proteolytically prepared material. This much higher resolution enables us to study in much more detail the interaction between antibody and antigen and refinement of the structure is in progress. 2. Triple-helix DNA. We are attempting to determine the structure of a DNA triplex. Crystals diffract to 2.9 A resolution. X-ray data have been measured and the structure determination is in progress. 3. MarA-DNA complex. MarA is a transcriptional activator of the mar operon that renders E. coli resistant to a variety of antibiotics. There is no structural information available about MarA, nor about the AraC subfamily, transcriptional regulators that have high sequence homology with MarA. We are currently investigating the crystal structure of MarA complexed with its DNA binding site. The complex has been crystallized, the crystals diffract to 2.9A, several heavy atom derivatives have been prepared and the structure determination is in progress.